1. Field of the Invention
The present invention relates to a head position control method, head position control device and disk device, for controlling the position of the head by compensating periodic disturbance, such as eccentricity, and more particularly to a head position control method, head position control device and disk device for implementing high track pitch and optimizing the inspection process.
2. Description of the Related Art
In a disk device which reads/writes data on a rotating recording disk, such as a magnetic disk device or optical disk device, accurately positioning a head to a target track, that is so called “following”, is extremely important to improve recording density.
For a recording disk, which rotates, on the other hand, positioning accuracy is decreased by such periodic disturbance as eccentricity and other non-periodic disturbance, so in order to implement high density track pitch, improvement of the position accuracy is required.
FIG. 16 is related diagram of the head position of the disk and position accuracy. As shown in the relational diagram of POS (Position) accuracy (TRO: Total Run Out) and the radius direction of the disk in FIG. 16, the POS accuracy is generally high, that is TRO is high, in the outer side on the disk because of the movement of the medium, and in the inner side, POS accuracy is low, that is TRO is low. Therefore it has been proposed to make the track pitch of the inner side different from that of the outer side on the disk plane (e.g. Japanese Patent Application Laid-Open No. 2002-237142 and 2003-016745).
However, if TPI is decreased, that is the track pitch is increased in the outer side, as the dotted line C in the relational diagram of the critical TPI (Track Per Inch) and the position in the radius direction of the disk in FIG. 16 shows, the track width increases. Therefore, the position of the head shifts due to vibration, and old data may not be converted into new data during write. In other words, two data may exist in the same LBA (Logical Block Address). Therefore the TPI lower limit at which data is changed is set, as the bold line A2 shows.
If the TPI is increased, that is the track pitch is decreased, in the inner side, as shown by the dotted line C in FIG. 16, on the other hand, the track space decreases and data on the adjacent track may be affected (e.g. data on the adjacent track is erased) when data is written on a track. Therefore the TPI upper limit is set based on ATI (Adjacent Track Influence) resistance, as the bold line A1 shows.
Also as the solid line B shows in FIG. 16, there is a TPI that must be satisfied as the average of all zones (called the average required TPI), so it is difficult to determine TPI according to the POS accuracy, as the dotted line in FIG. 16 shows.
TRO in the relational diagrams in FIG. 16 is the sum of RRO (Repeatable Run Out), which is a periodic disturbance, and NRRO (Non-Repeatable Run Out) which is a non-periodic disturbance. A post code technology to improve this RRO has been proposed (e.g. Japanese Patent Application Laid-Open No. H03-263662 and No. S60-117461).
As FIG. 18 shows, a sector of the magnetic disk 100 is comprised of a servo frame 101 and a data area 102. The servo frame 101 is further comprised of a preamble 110, servo mark 112, frame code 114, gray code 116 and burst signal 118. The frame code 114 and gray code 116 constitute a track number, and the burst signal 118 is a four phase burst (A/B/C/D) or a two phase burst (Even/Odd) signal, so as to recognize a position within a track by the head output.
By decreasing the burst area 118 of the servo frame 101, a post code 120 is assigned. After the magnetic disk 100 is mounted on the device, the magnetic disk 100 is rotated, and the eccentricity (RRO) in each sector is measured, and the eccentricity correction amount is written in the post code 102. When the disk device is operating, the servo frame 101 is read, the burst signal 118 and post code 120 are demodulated, the current position acquired from the burst signal 118 is corrected using the eccentricity correction amount of the post code 120, the current position including eccentricity is calculated, and head position is controlled so as to cancel the eccentricity.
By using this post code, the POS accuracy (TRO) in FIG. 16 is improved for the amount of RRO, and as the dotted line C1 of the relational diagram of the critical TPI and disk position in FIG. 17 show, the critical TPI can be improved from the original characteristic C, and high TPI can be implemented.